The invention relates to a catheter system for the transmission of laser radiation for treatment purposes, especially in vascular systems of the human body. It is known that certain deposits in vascular systems, for example of the human body, especially in blood vessels, can be detached by laser radiation of a certain energy density, presumably as a consequence of the photohydraulic effect, and the thus-treated vessels can therefore be recanalized. A catheter system for such applications has been disclosed, for example, in DOS No. 3,739,965.
Preferably, such catheter systems utilize an annular catheter with an inner duct around which inner duct the wall structure of the catheter retains a circular array of optical fibers for transmitting the laser light to the treatment site at the distal end of the catheter.
It is important in the design of such an annular catheter to ensure that the laser light exiting from the ring-shaped array of optical fibers impinges upon the deposits in the peripheral zone of the vessel which is to be canalized by the laser radiation. Therefore, the diameter of the ring-shaped lightguide arrangement has been chosen, in general, so that the lightguides are located along a peripheral circle corresponding approximately to the deposits. Such a catheter is then introduced into the vessel to be treated up to the point of constriction and can be advanced further only to the extent to which the deposits on the outer wall of the vessel have been removed by the treatment. In order to place the catheter in the right direction with progressing treatment and additional attempts at advancement, the inner duct provided in the catheter, or the lumen, is utilized. Besides being used as a flow channel for rinsing fluid, it can also for the insertion of a thinner guide wire which can be pushed forward even through the as yet untreated constriction sites. It then serves as a guide route for the further advancement of the annular catheter during the course of the treatment.
However, it is not always possible and therefore desirable to employ annular catheters with a diameter already corresponding extensively to the internal diameter of the vessel to be recanalized. It is desirable, especially for guiding a laser catheter forward into regions of a smaller vessel diameter, for example in the lower leg level of a patient or into cardiac coronaries, to utilize lightguide catheters having maximally small diameter which, if at all possible, is to range even below 5 French.
It can be derived, for example, from DOS 3,739,965 that, depending on the optical emergence characteristic of the distal end of the lightguide catheter, the energy density of the laser radiation decreases already with a small distance from the emergence surface to such an extent that it is no longer sufficient for an effective removal of plaques in vessels. This can occur, in particular, when a relatively thin annular catheter is employed; when the deposits to be removed are located asymmetrically on one side, for example in a flaring portion of the vessel; or when such deposits are outside of the diametrical range of the catheter. In such cases, it may become unavoidable to replace the catheter utilized, as required, by a catheter having a larger or smaller internal diameter adapted to the respective lumen of the vessel.